Show Menu

Biology Midterm chapters 6-7 Cheat Sheet by

Energy, Enzymes & Biological Reactions

Principles of thermo­dyn­amics applied to reactions and process of cells. Allows insight into how cells handle energy transa­ctions.
System + Surrou­ndings:
Closed: no energy exchange Open: energy can be added or removed Every change produces either heat or work
For Thermo­dynamic Measur­ements:
Standard conditions pH=7, T=25 degrees C, 1 Atm, Pressure State usually constant under biological conditions
First law of thermo­dyn­amics:
Energy cannot be created or destroyed, but it can be changed from one form to another.
Second law of thermo­dyn­amics:
Whenever changes form, entropy increases. Whenever energy changes form, some energy is lost ( unusable by the organism. Energy is conserved as a whole, but not in any system doing work.
the sum of all chemical reactions in an organism a balance between reactions which release energy and those that require energy
food molecules broken down to release energy
complex organic molecules synthe­sized from simpler ones- energy input is needed
Guide metabolic pathways
Gibb's Free Energy:
Energy released that is available to do useful work
processes cocue without energy input, and increase entropy.
processes require energy input

Biological Order & Disorder

Energy flows into ecosystems as sunlight and exits as
Living organisms
Convert sunlight to chemical energy. Use this chemical energy to do work. Generate heat and disorder on the process (increases entropy)
may decrease in living things (living things show order), but the total entropy of the universe increases in the process
uses energy to create order but thus energy also creates disorder.

Free- Energy Change, ∆G

Gibbs Free energy G
the energy in a system that can do work. The change in free energy (∆G) during a reaction.
Whether the reaction will be
Sponta­neous and release energy (exerg­onic) or be Non sponta­neous and store energy (ender­gonic)
is the change in total energy (enthalpy)
is the change in entropy
is the temper­ature in kelvin (k=C+2­73.15)
the reaction is sponta­neous, exergonic, and provides energy for work.
speed up reactions, but don't change ∆G

Mitoch­ondria and ATP

Animals, plats, fungi, and most protists depend on mitoch­ondria for energy to grow and survive.
ATP forms in mitoch­ondria as stored chemical energy available to do cellular work
harvested from energy released in reactions that break down food molecules.

Cellular Respir­ation

Collection of metabolic reactions that breakdown food molecules and stores energy as ATP

Aerobic and Anaerobic respir­ation

Aerobic respir­ation:
Form of cellular respir­ation in eukaryotes and many prokar­yotes
Oxygen is needed in the ATP producing process
Anaerobic respir­ation:
Form of cellular respir­ation in some prokar­yotes
A molecule other than oxygen, such as sulfate of nitrate, is used in the ATP producing process


The removal of electrons from a substance
The substance from which the electrons are removed (The electron donor) is oxidized
Stored Energy is released


The addition of electrons to a substrate
the substrate the receives the electron ( the electron acceptor) is reduced
Energy is stored

Redox Reactions

Oxidation and reduction reactions always coupled Redox Reactions
Reactions that move electrons from a donor molecule and simult­ane­ously add them to an acceptor molecule

Summary: Cellular Respir­ation

Cellular respir­ation includes reactions that transfer electrons from organic molecules (such as glucose) to oxygen, and reactions that make ATP

Electrons carriers such as NAD+

move electrons from fuel molecule to cellular destin­ations

1st stage of Glycolysis

Enzymes break a 6-carbon molecule of glucose into two 3 carbon molecules of pyruvate
Some ATP is synthe­sized by substr­ate­-level phosph­ory­lation an enzyme catalyzed reaction that transfer a phosphate group from a substrate to ADP
Some electrons are carried away by NADH

2nd stage of Pyruvate oxidation

Enzymes convert the 3-carbon pyruvate into a 2-carbon acetyl group, which enters the citric acid cycle and is completely oxidized to carbon dioxide
Some ATP is synthe­sized during the citric acid cycle
Lots of reduced electrons carriers carry away electrons as NADH and FADH

3rd Stage Oxidative Phosph­ory­lation

High energy electrons are delivered to oxygen by a sequence of reduced electron carriers in the electron
Free energy released by electrons flow generates on H gradient by chemio­smosis
ATP synthase uses the H gradient as the energy source to make ATP

Substrate level Phosph­ory­lation

Occurs when enough energy is released in a reaction step to pass phosphate onto ADP

Glycol­ysis: Splitting Sugar in half

Glycolysis (Embde­n-M­eyerhof pathway) breaks 6-carbon glucose into two molecules of 3 carbon pyruvate in 10 sequential enzyme catalyzed reactions
Glycolysis takes place in the cystol of all organisms

Energy flow in glycolysis

The initial steps of glycolysis require energy 2 ATP are hydrolyzed
4 ATP are produced by substr­ate­-level phosph­ory­lation for a net gain of 2 ATP
The electron carrier NAD+ is reduced to NADH, which carries 2 electrons and a proton (H+) removed from fuel molecules

Pyruvate Oxidation and the Citric Acid Cycle

Active transport moves pyruvate into mitoch­ondria matrix where pyruvate oxidation and the citric acid cycle take place
Oxidation pyruvate generates CO acetyl­-co­enzyme A(acet­ylcoA), and NADH
The acetyl group of acetyl-COA enters the citric acid cycle

Overview of citric acid cycle

Citric acid cycle, carbon products of pyruvate oxidation are oxidized to CO
All viable electrons are transf­erred to 3NAD+ (NADH) and 1FAD (FADH
Each turn of the citric acid cycle produces 1 ATP by substr­ate­-level phosph­ory­lation

Summary: The citric acid cycle

The eight reactions of the citric acid cycle (trica­rbo­xylic acid cycle, or krebs cycle) oxidize acetyl groups completely to CO generate 3 NADH and 1 FADH and synthesize 1 ATP by substrate level phosph­ory­lation
1 acetyl­-CoA+3 NAD + 1 FAD + 1 ADP + 1Pi + 2H

Oxidative Phosph­ory­lation ETS & Chemio­smosis

High energy electron removed from fuel molecules and picked up by carrier molecu­les-are released into the electron transfer system of mitoch­ondria

Mitoch­ondrial electron transfer system (ETS)

Series of electron carriers that altern­ately pick up and release electrons and ultimately transfer them to their final accept­or-­oxygen

Electron Flow

Individual electron carriers of the ETS are organized specif­ically from high to low free energy
NADH and FADH contain the most free energy and are easily oxidized
The terminal electron acceptor (O ) is most easily reduced
Electron movement through the system is sponta­neous, releasing free energy
Electron Transfer System from high to low free energy

Energy Flow in the ETS

In the ETS electrons release free energy used to build the H gradient across the inner5 mitoch­ondrial membrane
High H concen­tration in the inter membrane compar­tment
Low H concen­tration in the matrix
The H gradient supplies energy that drives ATP synthesis by mitoch­ondria ATP synthase

Transfers Between Proteins

Two small, mobile electron carriers, cytochrome C and ubiquinone (coenzyme Q) shuttle electrons between the major complexes


Proteins with a neme prosthetic group that contains an iron atom that accepts and donates electrons

Forming the H Gradient

Ubiquinone and complexes I, III, and IV actively transport protons (H ) from matrix to inter membrane compar­tment
Concen­tration of H in the inter membrane compar­tment generates an electrical and chemical gradient across the inner mitoch­ondrial membrane

Proton­-motive force

Stored energy produced by proton and voltage gradient
Energy is used for ATP synthesis and cotran­sport of substances to and from mitoch­ondria

ATP Synthase and Chemio­smosis

In the mitoch­ond­rion, ATP is synthe­sized by ATP synthase, an enzyme embedded in the inner mitoch­ondrial membrane
The H gradient powers ATP synthesis by ATP synthase by chemio­smosis
ATP synthase uses proton­-motive force to add phosphate to ADP to generate ATP (phosp­hor­yla­tion)

ATP synthase structure and function

A basal unit in the inner membrane is connected by a stalk to a headpiece located in the matrix- a peripheral stator bridges the basal unit and headpiece
Proton­-motive force moves protons in the inter membrane space through the enzyme's basal unit into the matrix
H flow powers ATP synthesis by rotation of the ATP synthase headpiece (chemi­osm­osis)

Conser­vation of chemical Energy

Hydrolysis of ATP to ADP yields about 7.0 kcal/m­ol-­total energy conserved in 32 ATP is about 224 kcal/mol
Glucose burned in the air releases 686 kcal/mol
Efficiency of cellular glucose oxidation (224/6­86*100) = 33%
The rest of the chemical energy is released as body heat

Fermen­tation can re-oxidize NADH

When oxygen is absent or limited, electrons carried by the 2 NADH produced by glycolysis may be used in fermen­tation
Otherwise, glycolysis will stop due to lack of NAD
Recall:NAD accepts electrons in reaction 6 of glycolysis


Electrons carried by NADH are transf­erred to an organic acceptor molecule (convert NADH to NAD )
Glycolysis continues to supply ATP by substrate level phosph­ory­lation

Lactate fermen­tation

Converts pyruvate into lactate
Occurs in some bacteria, plant tissues, skeletal muscle
Used to make butter­milk, yogurt, dill pickles

Alcoholic fermen­tation

Converts pyruvate into ethyl alcohol and CO
Occurs in some plant tissues, invert­ebr­ates, protists, bacteria, and single­-celled fungi such as yeasts
Used to make bread and alcoholic beverages

Interr­ela­tio­nships of Catabolic Anabolic Pathways

Many carboh­ydr­ates, lipids, and proteins can be hydrolyzed and their products are directed into various stages of cellular respir­ation to be oxidized as fuel
CoA directs products of many oxidative pathways into the citric acid cycle

Oxidation of Fats

Oxidation of fats produces more than twice the energy of oxidation of proteins or carboh­ydrates
Before entering oxidative reactions, trigly­cerides are hydrolyzed into glycerol and individual fatty acids

Oxidation of proteins

The amino group is removed
The remainder enters oxidative pathways as pyruvate, acetyl­-CoA, or interm­ediates of the citric acid cycle

Many Pathways Start Glycolysis or the Citric Acid

Glycolysis and the citric acid also supply molecules from which many other cellular molecules are synthe­sized
Additi­onally, when energy is not needed by the body, glucose can be synthe­sized from interm­ediates of these pathways in the process of glucon­eog­ensis
Glucon­eog­enesis: which consumes ATP rather than producing it

Glycolysis and Citric acid Cycle Regulation

ATP and NADH production are balanced against glucose conser­vation by systems that regulate enzymes of glycolysis and the citric acid cycle
If excess ATP is present in cytosol, ATP binds to phosph­ofr­uct­okinase (in reaction 3) slowing or stopping enzyme action by feedback inhibition in order to regulate glycolysis
If excess ATP or citrate is present in the mitoch­ondria, one of these binds to citrate synthase, slowing or stopping enzyme action by feedback inhibition in order to regulate the citric acid cycle


No comments yet. Add yours below!

Add a Comment

Your Comment

Please enter your name.

    Please enter your email address

      Please enter your Comment.

          Related Cheat Sheets

          AP Biology Unit 1: Biochemistry Cheat Sheet
          AP Biology Unit 2: The Cell and Cell Membrane Cheat Sheet

          More Cheat Sheets by martinna